1. Field of the Invention
The invention relates in general to an image scanning method and a scanning device thereof, and more particularly to a sheet-fed image scanning method capable of protecting the to-be-scanned sheet and obtaining high-quality scanned image and a scanning device thereof.
2. Description of the Related Art
Scanner is an electronic input device with a wide range of application. The critical components of a scanner include a scanning module and a mechanical transmission portion. Due to the simple structure of the mechanical transmission portion, the sheet-fed scanner can be miniaturized and become a portable input device. The sheet-fed scanner normally adopts a contact image sensor (CIS), which is still with respect to the body of the scanner, and the to-be-scanned document is scanned relative to the movement of the body of the scanner. The method is suitable for small-sized scanners such as portable scanning device for scanning small-sized documents such as photos, checks, business cards, and so on.
Such type of scanning normally adopts sheet-feeding rollers to provide the to-be-scanned sheet with power for feeding paper. The sheet-feeding rollers are located under the scan window of the CIS scanning element. When the to-be-scanned sheet is continually fed in by the sheet-feeding rollers, the sheet-feeding rollers enable the to-be-scanned surface of the to-be-scanned sheet to always have frictional contact with the scan window glass at the scan window. As the friction is large in sliding, when the to-be-scanned document is thick such as a photo and the scanning surface of the to-be-scanned document has an adhesive surface, large friction may occur between the adhesive surface of the photo and the scan window glass so as to scratch or damage the photo. On the other hand, the CIS scanning element is elastically connected, and the ascending/descending of the CIS scanning element can be adjusted according to the thickness of the to-be-scanned sheet. Therefore, the CIS scanning element is always shaking when performing scanning, and may easily result in blurred scanned images but hardly obtain high-quality scanned images.